Spectral zonal photography using color-coded photostorage in a color blind panchromatic storage medium

ABSTRACT

This invention relates to spectral zonal photography in which spectral zones of a scene are stored with unique respective carrier modulations on a colorblind photostorage medium such as a black-and-white panchromatic film from which the scene can be reconstructed in color by Fourier transform techniques with spatial and spectral filtering, and in particular to methods and means to effect such storage without the intervention of a plurality of separate individual images of the scene. Each of several spectral zones is modulated with a periodic function, such as a grating having a unique orientation relative to the scene. Embodiments are disclosed in which these zones and their respective modulations can be stored in sequence or simultaneously. Unique spectral zonal filters are disclosed for simultaneous storage of several spectral zones of a scene. In one aspect of the invention such filters can be employed in direct contact with the storage medium. In another embodiment, Fourier transform techniques are employed with spatial and spectral filtering to effect simultaneous storage of several spectral zones of a scene. In all embodiments the final storage of colorcoded information in a colorblind storage medium is useful to reconstruct the original scene in the original colors or in any desired portion or portions of the visible spectrum by means of Fourier transform and filtering techniques. The reconstructed scene can be viewed in full color or recorded on a color sensitive medium.

United States Patent Continuation of application Ser. No.

564,340, .Iuly II, 1966, now abandoned.

[54] SPECTRAL ZONAL PHOTOGRAPHY USING COLOR-CODED PHOTOSTORAGE IN ACOLOR BLIND PANCIIROMATIC STORAGE MEDIUM 32 Claims, 17 Drawing Figs.

[50] Field of Search 355/2, 32, 33, 71; 350/162, I64; 352/45; 340/173 52u.s.c| 355/2, 340/173, 350/l62, 350/l64, 352/45, 355/71 [5 1] Int. ClG03!) 27/32 [56] References Cited UNITED STATES PATENTS 3,3 14,05 2 4/ l967 Lohmann (BLUE) Primary ExaminerSamuel 8. Matthews AssistantExaminer-Richard A. Wintercorn Attorneys-Rosen and Steinhilper and JohnH. Coult storage without the intervention of a plurality of separateindividual images of the scene. Each of several spectral zones ismodulated with a periodic function, such as a grating having a uniqueorientation relative to the scene. Embodiments are disclosed in whichthese zones and their respective modulations can be stored in sequenceor simultaneously. Unique spectral zonal filters are disclosed forsimultaneous storage of several spectral zones of a scene. In one aspectof the invention such filters can be employed in direct contact with thestorage medium. In another embodiment, Fourier transform techniques areemployed with spatial and spectral filtering to effect simultaneousstorage of several spectral zones of a scene. In all embodiments thefinal storage of color-coded information in a colorblind storage mediumis useful to reconstruct the original scene in the original colors or inany desired portion or portions of the visible spectrum by means ofFourier transform and filtering techniques. The reconstructed scene canbe viewed in fuil color or recorded on a color sensitive medium.

P NTEmuuzzmn 3.586.434

sum 3 or a FIG. 4A

l. g Qelvr #2011811 "A O @"Bllibl I f v I SPECTRAL ZONAL PHOTOGRAPHYUSING COLOR- CODED PI-IOTOSTORAGE IN A COLOR BLIND PANCIIROMATIC STORAGEMEDIUM CROSS-REFERENCE TO RELATED APPLICATION This application is acontinuation of application Ser. No. 564,340 filed on July I I, 1966.

BACKGROUND OF THE INVENTION The production of a true-colored image of acolor scene has engaged workers in the photographic arts almost sincethe beginnings of practical photography. Early attempts proceeded alongone path seeking a recording material which would produce the coloredimage directly, and along another path seeking to produce a record incolorblind (e.g.: blackand-white) recording material, from which atrue-colored image of the scene could then be produced. In theapproximately three-quarters of a century that has elapsed since firstrecords of these attempts appeared, success in making colorsensitiverecording material has been achieved to the point of availability to thegeneral public, but complex technical problems have confined to thelaboratory and to industrial usages processes which provide a coloredimage through the medium of colorblind records of color values of theoriginal scene. Outstanding of these problems has been the need to makea separate record for each of the primary colors (usually three) fromwhich the colored image is synthesized, with the attendant problem ofregistering the separate records in the colored image.

The problem of making the separate records was also attacked withphysical as well as chemical techniques. An early example of the use ofdiffraction gratings to code" three primary color values of a scene isdescribed in the British Journal of Photography, Aug. 3, 1906, pages609-612 by Herbert E. Ives Improvements in the Diffraction Process ofColor Photography. The background process of Prof. R. W. Wood (I899)using three gratings of different periodicities, is described in Wood'sUS. Pat. No. 755,983. Neither Wood nor Ives succeeded in avoiding theneed to make a plurality of separate color records; their gratingconfigurations were complex and could not be made on one plate; attemptsto do so led to even more complex gratings crossed with Joly lines; andthe reproduction apparatus did not pass very much light to the eye.

Carlo Boccas US. Pat. No. 2,050,417 discloses a process employingdiffraction gratings to encode color information on black and whitestorage media in a manner which makes possible improved illumination inthe reproduction of the colored image. But, as do Wood and Ives, Boccabegins with three separate images of the original scene (i.e.: threepartial negatives of the subjectfirst taken through three coloredfilters"), and fails to avoid the attendant registration problem.

OBJECTS OF THE INVENTION It is a principal object of the presentinvention to provide methods and means to record, overlapping each otherin a selfregistered configuration on the same area of a black-andwhiteor other monochromatic photostorage medium, a plurality of color-codedimages of a single scene, without the need for making two or moreseparate or partial records of the scene, each image being uniquely somodulated with colorcoded information that it can be spatially separatedfrom the others by Fourier transform techniques.

A further object of the invention is to provide methods and means so toencode color information on a black-and-white storage medium in anordinary camera, in the same way that an ordinary photograph or snapshotis taken, so that the invention may be made available to the generalpublic.

Additional objects of the invention are to provide a storage technique,and means to carry it out, by which the color information will be ofenhanced purity, and cross-products of two or more separate color valueswill be minimized; and to provide improved reproduction of color imagesof the original scene.

These and other objects and features of the invention will becomereadily apparent from the following description of several embodiments.This description refers to the accompanying drawings, wherein:

FIG. I illustrates the steps of a process for sequentially storingspectral zonal information for three separate zones with unique periodicintensity modulations in a singleblack-andwhite storage medium;

FIG. 2 schematically illustrates the separate spectral zonal imagesstored by the individual steps of FIG. 1;

FIG. 3 schematically illustrates the final storage of three spectralzonal images obtained with the process of FIG. I;

FIG. 4A illustrates a spectral zonal filter of the subtractive ornegative type suitable for simultaneous storage of three spectral zonesof a scene with unique periodic modulations in a black-and-white orother color-blind" but panchromatic storage medium;

FIG. 4B is a graph illustrating the ideal transmissivities of the filterelements of FIG. 4A;

FIG. 5 illustrates the use ofthe filter of FIG. 4A in an ordinarycamera;

FIG. 6 is a graphical illustration of a density versus log exposurecurve for reversal processing of photographic films, useful inexplaining a technique which may be employed in practicing theinvention;

FIG. 7 is a graphical illustration of double negative processing toobtain the results of the reversal processing of FIG. 6;

FIG. 8 illustrates a system for reconstructing color images by means ofa Fourier transform of the stored record and spatial and spectralfiltering, along the general lines suggested by Boccas Pat. No.2,050,417;

FIG. 8A is a detail sketch illustrating the use of a spatial andspectral filter in FIG. 8;

FIG. 8B is a detail sketch illustrating an alternative spectral andspatial filter;

FIGS. 9A and 9B are schematic illustrations of two cameras, similar inprinciple, for making a multispectral zone image in colorblind storagematerial by Fourier transform techniques applied to an image of thescene followed by spatial and spectral filtering;

FIG. I0 is a detail sketch illustrating the Fourier transformconfiguration used in the systems of FIGS. 9A and 9B; and

FIG. II is a set of detail sketches illustrating the process ofcolor-coding used in the systems of FIGS. 9A and 98.

For the purposes of the present disclosure, the basic equation for acolor scene may be described as:

(Relation I) Where:

I (g, X) represents the intensity distribution of light over the sceneas a function of spatial coordinates and wavelength (A); and

II represents the intensity distribution in the wavelength band A, as:1. function of spatial coordinates s); and

X, is t he average wave length in the hand from i A);

to M iii) This basic equation describes the energy distribution in theimage plane of a camera. When the color components are blue, green andred, the energy distribution is the sum of three components at eachpoint in the scene.

In the final storage of color-coded information in a colorblind (e.g.:black-and-white) recording from which the original color scene can bereconstructed, one would like the storage to be according to thefollowing equation:

(a M-"(e n meen.

(Relation 2) Where: l,,.(x,x)-1r(x,lt) represents the intensitydistribution I,,,(x,}\) multiplied by the total periodic modulation (11)of the periodic modulations on all wavelength bands as a function ofspatial coordinates (x) in the scene and wavelength (A); and

M2)- W2)! represents the intensity distribution in the wavelength bandA; as a function of spatial coordinates (x) multiplied by the periodicmodulation (P) of the light in that band as a function of spatialcoordinates (x) with the azimuthal characteristic 01,-. It will beunderstood that the wavelength bands can be blue, green and red, and theperiodic modulations can be given azimuthal characteristic oriented atangles aa-l-1r/3 and a+21rl 3, respectively, as one fairly obviousexample, in which case Relation 2 would take the form:

"'I Z-PJI 1 .lZ-Pll l (J l g L) (all (Relation 2A) Referring to FIGS. 1and 2, an object 10, which for the sake of illustration may be aphotographic color transparency in which there is a two-dimensionalimage represented by the double-headed arrows 11 and I2, is imaged byoptical means represented by lens 13 onto a colorblind photostoragematerial 14, a suitable example of which is panchromatic black and whitephotographic film, preferably of the high contrast and high resolutionvariety. The object 10, optics 13 and photostorage material 14 remainfixed relative to one another throughout the process about to bedescribed. The source of light (not shown) may be any available whitelight, such as daylight. As shown in FIG. 1A, a blue filter 16 isinterposed between the object and photostorage material 14, and adiffraction grating 15 is interposed between the filter and thephotostorage material, for example, directly on the photostoragematerial. The diffraction grating may be any suitable grating ofperiodic opaque and transparent regions, for example, in theconfiguration of a Ronehi ruling having opaque lines 15.1 ona-transparent support. The showing in FIG. I is exemplary only and doesnot represent any particular form of grating.

The grating can be placed at various locations between the object 10 andthe photostorage material 14 as long as the grating and the object areimaged as a product in the photostorage; that is, the object 10 and thegrating 15 should be optically multiplied in the photostorage material14, and not merely added therein. This can be done, for example, byplacing the grating directly in contact with the photostorage material14. The image which is recorded by incoherent illumination through theblue filter 16 will then be the product of the intensity due to bluelight as a function of the coordinates (x) in the recorded'image and, inthe present illustration, the periodic variation of the grating 15 in asingle dimension (x) oriented in a prescribed azimuthal direction (a),as indicated at 26 in FIG. 2 immediately beneath FIG. 1A.

FIG. 1B is identical to FIG. 1A except that a green filter 17 has beensubstituted for the blue filter and the grating 15 has been rotated inazimuth 60 (11/3) about the axis of the system. Another exposure of theobject 10 is then made, which records another image in the photostoragematerial 14 as shown at 27 in FIG. 2, immediately below FIG. 1B. Thisimage is mathematically described as the product of intensity due toexposure of the object through the green filter 17 as a function of thespatial coordinates (x) and the periodic function of the grating in asingle dimension (x) oriented in the azimuthal direction a+1r/3. A thirdexposure is then made as illustrated at FIG. 1C through a red filter 18with the grating 15 rotated a further 60 (21r/3) degrees to place on thephotostorage material 14 a third image illustrated at 28 in FIG. 2immediately below FIG. 1C, which is mathematically described as theproduct of the intensity of the exposure of the object 10 through thered filter 18 as a function of spatial coordinates (x) and the periodicvariation of the grating in a single dimension (x) oriented in theazimuthal direction a t2rr/3.

These three exposures are added in the final bIack-andwhite storage 29,which is schematically illustrated in FIG. 3, where the double-headedarrows l1 and [2 representing the original object have been reproducedand the grating images 26, 27 and 28 are superposed in the samerecording area. The mathematical sum of the three products shown in FIG.2 is set out under FIG. 3. This is the final storage of color-codedinfor mation in the colorblind (black-and-white) image, according torelation 2, from which the original color scene can be reconstructed byFourier transform techniques and spatial and spectral filtering. Thestored image 29 is desirably a transparency.

The system illustrated in FIG. I has the virtue not heretofore availablethat the scene being photographed, the recording medium on which it isbeing photographed, and the optical elements which focus the image ofthe scene on the recording medium, all remain fixed relative to eachother throughout the entire process of recording the coded imagesrepresentative of the color bands into which the scene is broken down.Thus, since separate color coded images are not made on separate piecesof recording media, the problem of registering such images iseliminated. The final color-coded black-and-white record shown in FIG. 3is obtained directly, without the intervention of the separate recordsof elemental color-coded images. The three diapositives mentioned inBocca Pat. No. 2,050,4 I 7, for example, are eliminated completely.

FIG. 4A illustrates a negative color filter consisting of thesuperposition of three colored Ronehi rulings having respective uniqueazimuthal characteristics, e.g: rotated in 1r/3 increments from oneanother. FIG. 4B shows ideally the required spectral transmissions ofthe respective rulings. A first array of bars 45 of width b" in FIG. 4Arepresent yellow bars, with transparent bars of width a" intervening;these comprise a yellow Ronehi ruling having periodicity P (x), whichgenerally is represented mathematically by I P,,(x)a,,. Similarly, amagenta ruling 46 is generally represented by m( m; and a cyan ruling 47is generally represented by modulations as a function of spatialcoordinates (x) and wavelength A is:

Where:

1r(x,) represents the product of the periodic yellow, magenta and cyanmodulations as a function of spatial coordinates (x) and wavelength (A).FIG 4A shows a special case of Relation 3. At a first glance, it mightnot appear that multiplication of Relation I with Relation 3 would yieldrelation 2. For example, the blue term in relation 2 would appear tocome out:

When it is realized, however, that the magenta and cyan filters eachtransmit blue, and that the blue light does not see" these filters, itis apparent that the terms involving P,,, and P should not appear inpractice. Ideally, the transmittance of blue through magenta and cyanfilters is unity, in the sense that the magenta and cyan filters are nota function of the spatial coordinates (x) for blue; thus, the terms P,,and P, are constants with relation to (x), and have a value of unity foran ideal dye, so that, for practical purposes we can set:

e e e aola (Relation 4;)

m That is, the blue light is modulated, essentially, only by the yel-(Relation 5) flawa)= (2)- (e) (Relation 6) T-Ibfidinultirilizitibriofthe scene relation 1) with the negative filter (relation 3 yieldsRelation 2 in the form: Ms) (9 (Relation 2B) The negative" color filterconsists of negative or subtractive color dyes on a background which maybe transparent to white light.

Multiplicative filters according to FIG. 4A may be made by the processillustrated in FIG. 1, using any commercially available three-layercolor film, of which Ektachrome or Kodacolor" (Eastman Kodak Co.),Anscochrome" (General Aniline and Film Co.), or Agfacolor" (AgfaAktien-i gesellschaft Leverkusen-Bayerwerk), are representativeexamples. Ektachrome has been found to be particularly suita- 535Ektachrome is constituted of three layers having, respectively, yellowdye (minus blue), magenta dye (minus green) and cyan dye (minus red).Following a scheme according to" ble. A filter has been made from it, asis now described.

FIG. 1 using a Ronchi ruling, a piece of this film was exposed through ablue color filter as in FIG. 1A, then through a green color filter as inFIG. 1B, and then through a red color filter as in FIG. 1C. The piece offilm thus exposed was developed, not as a reversal film as is ordinarilydone, but by the Kodak Color Process C-22, available from Eastman KodakCompany, Rochester, New York, for their negative films Kodacolor" andEktacolor. The use of Process C-22 to produce a negative from Ektachromeis known in the open literature. By this I process, the yellow layerproduces yellow grating lines in response to the blue light, the magentalayer produces magenta lines in response to the green light, and thecyan layer produces cyan lines in response to the red light. White lineswere produced in each layer wherever the Ronchi ruling was black. Thisprocess produced exactly the multiplicative filter which is illustratedin FIG. 4A. A similar filter can be made using Anscochrome anddeveloping by Kodak Color Process C-22. Kodacolor and Agfacolor filmsare also useful, but

these have a bright yellow background which may be objectionable.

While the filter of FIG. 4A is illustrated as composed of simpleharmonic to a square wave, can be used. The spatial frequency (w, inlines/mm.) of each grating used in any emvenient in FIG. 4A because oftheir relative simplicity and '75 because they allow a high degree oflight transmission while providing effective color-code modulation. 1

A suitable relationship is Ronchi rulings, the gratings need not belimited to this configuration. Filters constructed of any periodicfunction, from i the same general lines as the negative filter of FIG.4A, em- 1 ploying three superimposed gratings in the form of Relation 3,but with red, green, and blue substituted for their respective negativecolors, and with black or opaque spaces between the color lines.However, multiplication of such a positive" filter with a color scenewill approximate an expression like Relation 2 only if the color line(slit) widths (a) of each grating are very narrow compared to the periodlength p of the grating.

Such a color filter will require resolution, in the black-andwhitephotostorage medium, on the order of 5m, to 10m depending in thespectral purity required, and the speed of the photostorage medium willbe effectively reduced by the most severe filter factor (on the order of10-15 for the blue zone). However, use of this positive filter wouldpermit certain freedoms in photostorage, as will be explained below.

The negative" filter of FIG. 4A, or the corresponding positive" filterdescribed above, can be multiplied with a scene and the individuallymodulated color products can be summed in a photostorage medium simplyby placing the filter in a camera in contact with a piece of black andwhite panchromatic film, as is illustrated in FIG. 5. In thisillustration a camera 50 is shown having a photographic plate 51 in thefilm plane of its lens 54, the scene being represented by an 1 object52. A suitable filter 53 (negative" according to FIG.

4A or positive" as described above, for example) is shown in contactwith the plate 51. The photographic plate has only one photostoragelayer on it. The exposures through the three gratings of the filter aretherefore simultaneously added in the The sum of images stored in aconfiguration according to FIG. 3, whether by serial addition accordingto FIG. 1, or by simultaneous addition, as illustrated for example inFIG. 5, can be separated by Fourier transform techniques with partiallycoherent polychromatic light. Bocca Pat. No. 2,050,417 suggests in itsFIG. 6 a system for performing the separation, in which the storedblack-and-white imageis the projection positive located at positionA-B-C -D. Bocca illustrates in his FIG. 4 an idealized representation ofdiffraction orders along the primary axes of diffraction due to thethree gratings stored in the projection positive. In practice, however,I have found that, due mainly to nonlinearities in photographicprocessing of the black-and-white color-coded storage image, thisidealized representation is not achieved, but instead, crossproductsappear along axes parallel with the primary axes. These cross-productscan cause degradation in the reproduction of the original color sceneunless steps are taken to minimize their effects. Use of a narrow-linegrating, as in the positive" filter l have described above, or with verywide Degradation of the reconstructed image due to crossproducts in theFourier transform of the color-coded blackand-white stored image can bereduced to insignificance by processing the black-and-white storageimages so that the amplitude transmission in the stored image islinearly proportional to the input intensity (i.e.: exposure) inrecording the image. If this is done, the cross-products are eliminatedand the separation of color zones in the transform plane ismathematically exact, and the storage film need only resolve thefundamental carrier frequency.

It has been found mathematically that the cross-products can beeliminated by making the amplitude transmission of the objecttransparency linearly proportional to the input intensity (exposure) bywhich the exposures were made. To obtain this result requires ananalysis of the density-versus-log exposure curve for photographicmaterial. A conventional equation for the intensity transmission of aphotographic transparency when exposures are restricted to thestraightline portion of the D-log E curve is:

- TI =KI where K 10 f, The amplitude transmission for the transparencycan be stated TA( 1( In these equations: Tr(m) is the intensitytransmission; K isa constant Hz) is the intensity distribution of animage formed by uniformly illuminating a. transparency;

y is the slope of the density-versus-log exposure curve; D is the basedensity of the photographic material;

T (1:) is the amplitude transmission.

The equation for amplitude transmission can be made linear with inputintensity transmission by setting gamma equal to 2. It must berecognized, however, that for this to have any valid effect the gammashould also be constant. For example, it becomes important that no imageexposure be made in a nonlinear portion of the density-versus-logexposure curve.

In processing the images for a constant gamma of 2, it is necessary torelate this gamma to the coherence of the optical system. Measureddensity-versur-log exposure curves varywith the conditions ofmeasurement. Thus curves measured with a densitometer, amicrodensitometer, and in a coherent system may differ one from theothers. These differences are apparently due to differences in diffuseand spectral density which in turn relate to the graininess of thephotographic emulsion. For the present invention, the gamma should bedetermined by measurement in an optical system of the same degree ofcoherence as is used to reconstruct and display the colored images.

The following two examples illustrate specific methods that have beenused in practicing the invention.

' EXAMPLE I The photographic plate 51 used in the camera 50 had areversal process density-versus-log-exposure curve with a gamma of --2as illustrated in FIG. 6. The plate was uniformly preexposed so that theobject exposures fell in the straight portion of the exposure curve. Themaximum total exposure was limited so that this also did not go beyondthe straight line portion of the curve.

The original colored image was reconstructed and read out in thecoherent system of FIG. 8. The displayed image was of true color andgood quality with no noticeable ghosting of the cross-product imagesobservable upon close scrutiny.

EXAMPLE II Exposures were made the same as in Example 1 but using a film51 processed to a gamma of minus one-half as shown by represented bycurve 40. Thus the output amplitude transmittance is proportional to theinputexposure. This transparency was displayed in a coherent systemaccording to FIG. 8 with results similar to those in Example 1.

FIG. 8 illustrates diagrammatically an optical system for reconstructingand viewing or recording colored images that are stored inblack-and-white as described above. FIG. 8 illustrates a fairlyconventional partially coherent optical system comprising a light source60, pin hole aperture 61, light collector lens 62, converging (ortransform) lenses 63 and 65 separated by the sum of their focal lengthsf, and f2, frame means 66 for supporting the color-coded black-and-whitetransparency 29 and support means 67 for supporting a photosensitivecolor medium or a display screen. A color reconstruction filter 68,details of which are shown in FIG. 8A, is located in the back focalplane of the first transform lens 63 and the front focal plane of thesecond transform lens 65. For simplicity of illustration, only thegrating modulation lines at three different angles are shown in theblack-andwhite stored image 29, but it will be understood that thisimage is a transparency containing original object information as wellas grating information.

For purposes of the invention, light source 60 should be an intensepolychromatic light source; an arc lamp will be suitable.

The pin hole aperture 61 is used to increase the coherency of the lightand the collector lens 62 following the aperture can provide a lightbeam of a selected diameter for illuminating the system. With acollimated light beam the distance between the collector lens and thefollowing components of the system becomes noncritical. With anuncollimated light beam magnification can be obtained.

The color reconstruction filter 68 in the back focal plane of the firstlens 63 is located in the Fourier transform plane. The

light beam from the collecting lens 62 is brought to a point focus atthe transform plane. The light from the source 60 must be at leastpartially coherent at the illumination plane where the stored image 29supported in frame 66 is illuminated. The required degree of coherenceis related to the carrier frequency. Preferably the coherence interval(the distance between two extreme points in a light field which stillexhibit interference) should be equal to or greater than a few periodslengths of the carrier frequency.

With the black-and-white color-coded stored image 29 positioned in frame66, a diffraction pattern will appear in the transform plane. Thisdiffraction pattern is depicted at the location of the colorreconstruction filter 68. Light from the I source 60 that is undisturbedby the recorded image 29 will be focused to the center of the transformplane as spot illustrated as the central illumination spot 70. This spotrepresents the zero order of each grating and is commonly called the DCspot. Since this spot is independent of grating orientation it will becommon to all of the individual color-band images superimposed in thestored image 29. A first series of spots 71 (shown vertically orientedin FIG. 8) represents diffraction orders of the horizontal gratingrelated, for example, to the blue exposure in FIG. HAL Extending out inboth directions beyond the zero diffraction order are the first andseveral higher diffraction orders.

The diffraction orders 72 related for example to the green exposure inFIG. 1B 'are in a line azimuthally rotated 60 clockwise from thediffraction orders 71, and the diffraction orders 73 related for exampleto the red exposure of FIG. 1C are in a line rotated azimuthally 60clockwise from the diffraction orders 72.

FIG. 8 shows only diffraction orders along the primary axes ofdiffraction. If appropriate steps are taken, as described above,cross-products will not appear along axes parallel with the primaryaxes.

Reconstruction of the original color scene is obtained by placing acolor reconstruction filter 68 as illustrated, for example, in FIG. 8Ain the transform plane of FIG. 8. The color reconstruction filter is, inthis illustration, opaque at the center 69, to block the DC spot 70.Arrayed about the center in diametrically-opposed pairs are six equalsectors of color filter material. A pair of blue filter sectors (8, B)are located in the path of light forming the diffraction orders 71related to the blue exposure, a pair of green filter sectors are locatedin the path of light forming the diffraction orders 72 related to thegreen exposure, and a pair of red filter sectors are located in the pathof light forming the diffraction orders 73 related to the red exposure(all referred, for example, to FIG. 1). A reconstruction, in full color,of the original scene 11, 12 appears in the plane of the support means67, where it can be recorded on color-sensitive photographic film, orobserved on a screen. This reconstruction would contain gratinglikeimages (fringes) since more than one diffraction order is passed on eachsector. By passing only one diffraction order through each sector or bydestroying temporal coherence between orders from each grating,continuous tone reconstructions may be obtained without the presence offringes. FIG. 8B shows a spectral and spatial filter 68A which passesone order through aperture 71a in one sector (blue), one order throughaperture 72a in a second sector (green), and one order through aperture73a in the third sector (red). The rest of this filter 68A is opaque.

FIG. 9A shows a camera system for multiple-zone recording of spectralinformation in a color scene. In this figure, the plane of the object110, corresponding to the object 10 in FIG. 1, is located by a pair oflines 111 and 112 crossing on the axis of the system. An ordinaryachromatic camera lens 113, fitted with an adjustable-iris stop 114,focuses an image 120 of the object in an image plane, which is locatedby a pair of lines 121 and 122 crossing on the system axis. Consistentwith notation familiar to workers in the art, the object may be termed(x), and the image may be termed I(y), where (x) represents the spatialcoordinates in the object plane and (y) represents the spatialcoordinates in the image plane. a

The components thus-far described are those found in a camera. Theobject plane-to-lens (iris stop) distance is p and the Iens-to-imageplane distance is q,, in accordance with the general relationship:

f the lens involved. In place of the usual film and back, however, thesystem of FIG. 9A has a special neutral density grating 130 in the imageplane. The plane of this grating is located in FIG. 9A by a pair oflines 131 and 132 crossing on the system axis. The special grating 130has, for the purposes of describing this embodiment, three-gratings in aconfiguration as shown in FIG. 4A, in which each grating is aone-dimensional black-and-white cosine ruling of spatial frequency (0and has an amplitude transmission represented by:

P(y)=a +b cos (0 1 where:

P (Y) represents the periodic modulation of the grating in one dimensionin the image plane, and

a b. For the three zone system under description the amplitudetransmission is:

Relation 7 resembles Relation 3, except that no tions are present inRelation 7.

Following the image plane and special grating 130 is a first transform(converging) lens 135 having focal length f located with the image planein front of it. Assuming the system is illuminated by partially coherentpolychromatic light (sunlight for aerial applications; extended tungstensource for laboratory applications), a transform of the special grating130 convolved with the image 120 will appear in the transform plane 140in the back of the first transform lens 135. The transform plane may bedesignated the (a) plane, and the image convolved with the grating maybe designated (a) (11). Two lines 141 and 142 crossing on the systemaxis locate the transform plane.

spectral func Relation 7) The Fourier transform of the special grating130, designated 7(a), is represented schematically is'FIG. 10, in whichthe relative intensity distributions in the zero and first orders areshown, but no spectral distribution is indicated. The zero order isrepresented by a spot 145. The first orders of the grating at a, arerepresented by spots 146; those of the grating at a, by spots 147; andthose of the gratings at a, by spots 148. Since the gratings are allsimple harmonic functions (cosine) the grating orders in the transformplane are delta functions, and no orders higher than the first orderappear; the spots 146, 147 and 148 represent the delta functionpositions of 7(a). The term t, in FIG. 10 represents the separation ofeach first order position from the zero order.

The amplitude distribution of the camera lens exit pupil (i.e. the irisstop (114) distribution) is replicated by the special grating 1r(y) soas to be convolved about each of the delta function positions in thetransform plane 140. When the iris 114 is stopped down so that thediameter of the iris image is 1., or less, these iris stop replicationimages become separated in the transform plane. This is shown moreclearly, and in greater detail in FIGS. 11A and 118.

In FIG. 11A the position of each first-order delta function spot in FIG.10 is taken by a series of smaller dots representing the spectraldistribution in the diffraction order. Thus, for example, three smalldots 146.1, 146.2 and 146.3 are shown for the grating at 01,,representing the centers, respectively, of the blue, green and red bandsof the spectrum, spaced [L from the zero order spot 145. The intensitydistribution bl4 for this entire first-order spot 146 is also shown.FIG. 118 shows the convolution of the exit pupil distribution about eachdelta function. Reference characters have been assigned to exit pupilimages 114.1 about dot 146.1, 114.2 about dot 146.2, and 114.3 about dot146.3, respectively. For the sake of simplicity, and because it is notnecessary to do so, additional reference characters have not beenassigned in FIGS. 11A and 11B. It is seen, however, that the Fouriertransform of the image convolved with the grating contains the colorinformation in the imaggpartially dispersed. a 7 7 Spectral bandlimiting of each of the three zones into which the image is separated bythe grating is achieved in the transform plane by introduction of aspectral filter 150, which is located in the transform plane. Thisfilter may be similar in construction to the filter of FIG. 8A, exceptthat it need not stop the zero order. The plane of this filter islocated by two lines 151 and 152 crossing on the system axis. Thisfilter is the first element in the system to introduce colorinformation, and it is therefore designated as S( ;1.,h a function ofboth spatial coordinates in the transform plane and of wavelength. As isindicated in FIG. 11C, this filter is multiplied with the Fouriertransform and passes red images from one grating, blue images fromanother grating, and green images from the third grating. The circlesdesignated 114.3 represent the red images which are passed from thegrating oriented at a The circles designated 114.2 represent the greenimages which are passed from the grating oriented at 01,. The circlesdesignated 114.1 represent the blue images which are passed from thegrating oriented at 01 If the zero order is passed, portions of it willbe shared by each color. While in this scheme the resolution is notidentical for all colors, and it is realized that the iris stop 114could be given a complex shape and spectral transmission to compensatefor this, it is not necessary to do so.

A second transform lens 155, of focal length f is located with thetransform plane in front of it, and a final image and/or film plane 160in back of it. This latter plane is located by a pair of lines 161 and162 crossing on the system axis.

The plane 160 located by dashed lines 161 and 162 crossing on the systemaxis is the plane where the image (I'(z would be if the second transformlens were not present. This plane is located a distance q from the firsttransform lens 135, while the image plane 120 is located a distance p infront of that lens. Plane 160' is located a distance p in front of thesecond transform lens 155, while the final image plane 160 is located adistance q in back of that lens. The iris stop H4 is located a distancep in front of the first transform lens 135, and the transform plane 140is located a distance q, in back of that lens-The image (I(z)) in thefinal image plane I60 may be described as:

where the P(z) components are modified forms of the cosine fringes (P(Y)), and the zonal components 1,,(z), 1 (2) and ln(z) form the image(y)= n(y)+ c(y)+ fl(y) (Relation As has already been described,color-coded images in the form of Relation 8 can be stored in acolorblind photostorage medium, from which, by spatial filtering withpolychromatic light and spectral filtering with a filter similar, forexample, to filter 68 (see FIGS. 8 and 8A), the individual spectralzones can be recombined to form a full color image of the originalobject. Thus, by merely placing a suitable black-and-white photostoragemedium (not shown) in the film plane 160, and suitably exposing it anddeveloping it, a color-coded blackand'white stored image having the sameproperties as that represented in FIG. 3 is subsequently obtained in acamera system according to FIG. 9A.

The system of FIGS. 9-11 has several advantages, and unique properties.It will be observed, first, that the special grating 130 is ablack-and-white grating contracted in a single layer of photographicmaterial. Color coding is not introduced until after this grating hasbeen convolved with the image. The color coding spectral filter 150 isphysically easier to construct than a multicolor grating. Since deltafunctions appear in the transform plane, it is possible to use severalgratings oriented closer together than 1r/3, so that the achievablenumber of zones is greater than three. The purity of spectral zoneseparation is not restricted to any particular color scheme and, indeed,it is envisioned that different narrow color zones within a smallsegment of the spectrum can be separately coded and viewed or recorded.Thus, if for research purposes one desires to investigate a narrowspectral zone, or even a line, within the blue or the red region forexample, this narrow zone or line can be coded with any desired colorand later viewed or recorded as represented by that coding color. Thisprovides a useful application for the invention in the study of anaurora, for example.

In a practical example which has been constructed according to FIGS. 9A,10 and 11, the spectral filter 150 was made for the conventionaltricolor zones (red, green and blue) using Wratten filters 025, 058 and047, respectively, with azimuthal characteristics a a, and 01respectively. Neutral density filters were also introduced along withthe color filters, to balance the exposure, to equalize the effects of:

a. spectral output of the illuminating source;

b. spectral transmission of the colored absorption filters; and

c. spectral response of the recording emulsion.

In the case of a tungsten source with Panatomic-X film, these N.D.filters are:

Red N.D.=0.50 with 025 Wratten Green --N.D.=0.40 with 058 Wratten Blue-N.D.==0.00 with 047 Wratten The DC spot 145 can be blocked, but, if itis not, the spectral filter 150 is more efficient, reducing the requiredexposure time for making the stored image and reducing the filmresolution requirements on the photostorage medium.

FIG. 9B shows another system which will accomplish the same purpose asthe system of FIG. 9A. Similar parts of both figures have the samereference characters. FIG. 9B omits the second transform lens 155 ofFIG. 9A, and the optical relationship p 2 and q' are altered. Theoptical distances p, and q,, and p, and q,,, are similar in bothfigures.

If the negative" color filter of FIG. 4A is substituted in FIG. 9B (forexample) for the special filter 1130, then the spectral filter 150 canbe eliminated, and the lens 135 can be used as a relay lens to reimagethe product of the image [(y) and the filter 1r( y, A) onto aphotostorage material located in the [(z) plane 160. This arrangementremoves problems (if any) which may be associated with maintaining thegrating in contact with the photostorage material.

The foregoing description of certain embodiments of the invention is byway of example only, and not intended to limit the scope of the appendedclaims. Thus, for example, while transmission gratings have beenillustrated as devices for modulating light with a periodic function,'itwill be understood that light modulation by reflection is includedwithin the scope of the invention. No attempt has been made toillustrate all possible embodiments of the invention, but rather only toillustrate its principles and the best manner presently known topractice it. Therefore, such other forms of the invention as may occurto one skilled in this art on a reading of the foregoing specificationare also within the spirit and scope of the invention, and it isintended that this invention includes all modifications and equivalentswhich fall within the scope of the appended claims.

Iclaim:

ll. Method of preparing a photostored record of a scene in aphotostorage material which has response to light in a prescribedspectral band but does not make a color record within said band of therecorded light, which record is suitable for producing by Fouriertransform and spatial and spectral filtering techniques an image of saidscene in prescribed colors which may be natural or artificial, whichrecord is made from "n" light components representing spectral zoneswithin said band of said scene where n" is an integer greater than one,said method comprising the steps of:

l. erecting in an image plane an image of said scene;

2. modulating the light of said image in each of said components with aperiodic function having a unique azimuthal orientation; 7

3. selecting a modulating spatial frequency for each of said lightcomponents which is substantially twice the highest scene spatialfrequency desired to be reconstructed from that component; and

4. forming in said photostorage material from the light of said image asso modulated a photostored record of the sum of the products of saidlight components each multiplied with its respective modulation.

2. Method according to claim I in which each of said periodic functionsis contained in a transmission grating which is located between saidscene and said photostorage material.

3. Method according to claim 2 in which said grating is locatedsubstantially in the image plane.

4. Method according to claim 3 in which the photostorage material isalso located in the image plane, the grating is in contact with thephotostorage material, and the image is projected onto the photostoragematerial through the grating.

5. Method according to claim 3'in which a transform of the gratingconvolved with the image spectrum is spectrally filtered to form saidphotostored record.

6. Method according to claim 3 in which each periodic function is asimple noncolor selective harmonic function, and a transform of thegrating convolved with the image spectrum is spectrally filtered to formsaid photostored record.

7. Method according to claim 2 in which the grating is a substantiallytwo-dimensional light filter having a plurality of n periodic functionseach extending throughout the area of said filter and having a uniqueazimuthal characteristic in the area of the filter for passing lightrepresentative of a unique wavelength band corresponding to a selectedone of said spectral zones, respectively, said functions overlappingeach other, the configuration of said functions being such that thelight transmittance of said filter is expressed as the product:

Where:

1r(x,) is the mathematical representation of the total filter withtransmittance a function of spatial coordinates x and wavelength A;

P; )l is the periodic function corresponding to the wavelength band Awith azimuthal characteristic A and x is the average wavelength in theband from X, A to M-ix,

8. Method of preparing a colorblind image transparency suitable forproducing a projected image of a scene in prescribed colors, which maybe natural or artificial, from n" light components representing spectralzones of light from said scene where n" is an integer greater than one,comprising the steps of providing a film plane contact color modulationfilter having a plurality of n unique periodic functions, each of saidfunctions having a unique azimuthal characteristic in the plane of thefilter and comprised of periodic color filter elements capable ofpassing light limited to a unique wavelength band corresponding to aselected one of said light components, respectively, the configurationof said functions being such that when the filter is transilluminatedwith an aerial color image of said scene the filter-color image productis expressed as:

selecting a spatial frequency for each of said periodic functions whichis substantially twice the highest scene spatial frequency desired to bereconstructed from the light component modulated by that periodicfunction; and

placing said filter in contact with a photographic film which haspanchromatic response to colored light but does not make a color recordthereof; exposing said film to said image through said filter; anddeveloping said film.

9. Method according to claim 8 in which said film is processed toprovide a transparency in which the amplitude transmittance issubstantially linearly proportional to the exposure.

10. A method according to claim 1 in which the photostored record is atransparency, including the further step of so forming said transparencythat when it is transilluminated its output amplitude transmittance issubstantially linearly proportional to the input exposure which formedsaid record.

11. A method according to claim 3 in which the image-grating product isreimaged onto said photostorage material to form said photostoredrecord.

12. A method of spectral zonal photography comprising:

exposing a photosensitive material responsive to radiation in allspectral zones desired to be recorded to an additive superposition ofspectral separation images formed in radiation propagating from aphotographed scene in at least three different zones of theelectromagnetic spectrum;

during the said exposure operation, causing a periodic grating functionto be multiplied with each of said separation images, said gratingfunctions having a different azimuthal orientation for each image;

selecting a spatial frequency for each of said grating functions whichis substantially twice the highest scene spatial frequency desired to bereconstructed from the spectral separation image multiplied with thatgrating function; and

developing the exposed photosensitive material to form a recordcontaining said separation images respectively modulating azimuthallydistinct spatial carriers.

13. A method as defined by claim 12 wherein said record comprises aphotographic transparency and wherein said developing operation is suchas to cause said transparency to have an amplitude transmittancecharacteristic which is substantially linearly proportional to theexposure which it received from the radiation forming said images.

14. A method as defined by claim 12 wherein said periodic arrays offilter elements are each spaced by substantially spectrally neutralelements, said filter elements in each array constituting asignificantly greater fraction of the period width than said neutralelements.

15. A method of spectral zonal photography, comprising:

exposing a photosensitive material responsive to radiation in allspectral zones desired to be recorded to a scene image multiplied with aspectral zonal encoder comprising at least three mutually coextensive,azimuthally distinct periodic arrays of filter elements each having apreferential absorption for a different spectral zone and thus eachmodulating a different color separation image; selecting a spatialfrequency for each of said periodic arrays of filter elements which issubstantially twice the highest scene spatial frequency desired to bereconstructed from the color separation image modulated by that array;and developing the exposed photosensitive material to form a recordcontaining said color separation images respectively modulatingazimuthally distinct spatial carriers. 16. A method of color photographyusing monochrome or other recording materials which 1 do not exhibit,when developed, recorded color values in color, comprising:

exposing a photosensitive material responsive to radiation in allspectral zones desired to be recorded to a scene multiplied with aspectral zonal filter comprising mutually coextensive, azimuthallydistinct periodic arrays of cyan, yellow, and magenta filter elements,said cyan, yellow, and magenta arrays respectively periodicallymodulating red, blue, and green color separation images; selecting aspatial frequency for each of said periodic arrays of filter elementswhich is substantially twice the highest scene spatial frequency desiredto be reconstructed from the color separation image modulated by thatarray; and

developing said photosensitive material to form a record containing red,blue, and green color separation images respectively modulatingazimuthally distinct spatial carriers.

17. A method as defined by claim 16 wherein said record comprises aphotographic transparency and wherein said developing operation is suchas to cause said transparency to have an amplitude transmittancecharacteristic which is substantially linearly proportional to theexposure which it received from the radiation forming said images.

18. A method as defined by claim 116 wherein said periodic arrays offilter elements are each spaced by substantially spectrally neutralelements, said filter elements in each array constituting asignificantly greater fraction of the period width than said neutralelements.

19. A method of spectral zonal photography and reconstruction,comprising:

exposing a photosensitive material to a scene multiplied with a spectralzonal filter comprising three mutually coextensive, azimuthally distinctperiodic arrays of filter elements each having a preferential absorptionfor a different spectral zone and thus each modulating a differentspectral separation image; selecting a spatial frequency for each ofsaid periodic arrays of filter elements which is substantially twice thehighest scene spatial frequency desired to be reconstructed from thespectral separation image modulated by that array;

developing said photosensitive material to form a record containingthree spectral separation images modulating azimuthally distinct spatialcarriers;

locating the developed record in a beam of light which is substantiallycoherent;

forming in a Fourier transform space a diffraction pattern of saidrecord including three angularly se arated Dirac delta function arrays,each array being convolved with a spectrum of spatial frequenciescharacterizing a different one of said color separation images;

selectively transmitting through said Fourier transform space at leastone spectral order of said spatial frequency spectra associated witheach of said images;

causing the radiation passed through said transform space in colorseparation each of said spectral orders to have a mean wavelengthconsonant with the color separation information carried; and

retransforming said transmitted spectra to thus produce at anoutput'plane a full spectrum aerial reconstruction of 10 thephotographed scene.

20. A method as defined by claim 19 wherein said record comprises aphotographic transparency and wherein said developing operation is suchas to cause said transparency to have an amplitude transmittancecharacteristic which is substantially linearly proportional to theexposure which it received from the radiation fonning said images.

21. A method as defined by claim 19 wherein said periodic arrays offilter elements are each spaced by substantially spec-- trally neutralelements, said filter elements in each array constituting asignificantly greater fraction of the period width than said neutralelements.

22. A method of color photography and reconstruction using monochrome orother recording materials which do not exhibit, when developed, recordedcolor values in color, comprising:

erecting a full color aerial image of a scene to be photographed at animage plane;

locating a color encoding filter at said image plane so as to bemultiplied with said scene image, said filter comprising three mutuallycoextensive, azimuthally separated periodic arrays of differentsubtractive primary filter elements, each periodic array modulating adifferent color separation image;

selecting a spatial frequency for each of said periodic arrays of filterelements which is substantially twice the highest scene spatialfrequency desired to be reconstructed from the color separation imagemodulated by that array;

exposing a photosensitive material to said image multiplied with saidfilter;

developing said material to form a record of said scene in which red,blue, and green color separation images are effectively impressed onspatial carriers having different azimuthal orientations; locating thedeveloped record in light which is substantially coherent;

forming in a Fourier transform space at least one diffraction pattern ofsaid record including three angularly separated Dirac delta functionarrays respectively convolved with spectra of said red, blue, and greencolor separation images; selectively transmitting at least one spectralorder of each of said arrays through said Fourier transform space; and

causing the light carrying said red, blue, and green color separationinformation to be predominantly red, blue, and green, respectively,whereby a full color aerial reconstruction of said scene is produced.

23. A method of color photography for recording color scenes onmonochrome or other recording materials which do not exhibit, whendeveloped, recorded color values in color, comprising:

locating at a recording plane a photosensitive material responsive toradiation in all spectral zones desired to be recorded;

effecting a multiple exposure of said photosensitive material by, insuccession, forming an image of said photographic object on saidphotosensitive material in radiation in each of a plurality of spectralzones to which said photosensitive material is responsive;

during each of said multiple exposures of said photosensitive material,locating at said recording plane a grating having a spatial frequencyresolvable by said photosensitive material;

selecting a spatial frequency for the gratingfor each exposure which issubstantially twice the highest scene spatial frequency desired to bereconstructed from the color separation image modulated by that grating;

causing the grating to have a different relative azimuthal orientationduring each exposure of said photosensitive material; and

developing the multiple latent color separation images thus formed insaid photosensitive material to produce a record containing a pluralityof additively superimposed color separation images each of whichmodulates a spatial carrier having a different azimuthal orientation.

24. A method as defined by claim 23 wherein said record comprises aphotographic transparency and wherein said development step is such asto cause said transparency to have an amplitude transmittancecharacteristic which is substantially linearly proportional to theexposure which it received from the radiation forming said images.

25. A method as defined by claim 23 wherein said grating comprises aperiodic array of alternately opaque and neutral areas, the opaque areaconstituting a significantly greater fraction of the period width thansaid neutral areas.

26. A method of color photography and reconstruction using monochrome orother recording materials which do not exhibit, when developed, recordedcolor valuesin color, comprising:

locating at a recording plane a photosensitive material responsive toradiation in all spectral zones desired to be recorded;

effecting a multiple exposure of said photosensitive material by, insuccession, forming an image of said photographic object on saidphotosensitive material in radiation in each of a plurality of spectralzones to which said photosensitive material is responsive;

during each of said multiple exposures of said photosensitive material,locating at said recording plane a grating having a spatial frequencyresolvable by said photosensitive material;

selecting a spatial frequency for the grating for each exposure which issubstantially twice the highest scene spatial frequency desire to bereconstructed from the color separation image modulated by that grating;

causing the grating to have a different relative azimuthal orientationduring each exposure of said photosensitive material;

locating the developed record in a beam of light which is substantiallycoherent;

forming in a Fourier transform space a diffraction pattern of saidrecord including three angularly separated Dirac delta function arrays,each array being convolved with a spectrum of spatial frequenciescharacterizing a difierent one of said color separation images;

selectively transmitting through said Fourier transform space at leastone spectral order of said spatial frequency spectra associated witheach of said color separation images;

retransforming said transmitted spectra;

causing the radiation passed through said transform space in each ofsaid spectral orders to have a mean wavelength consonant with the colorseparation information carried; and retransforming said transmittedspectra to erect at an output plane a full color aerial reconstructionof the photographed scene.

27. A method as defined by claim 26 wherein said record comprises aphotographic transparency and wherein said development step is such asto cause said transparency to have an amplitude transmittancecharacteristic which is substantially linearly proportional to theexposure which it received from the radiation forming said images.

28. A method as defined by claim 26 wherein said grating comprises aperiodic array of alternately opaque and neutral areas, the opaque areaconstituting a significantly greater fraction of the period width thansaid neutral areas.

29. A method of spectral zonal photography for recording color values onmonochrome or other recording materials which do not exhibit, whendeveloped, recorded color values in color, comprising:

erecting a full-color aerial image of a scene to be photographed at afirst image plane; locating a grating at said first image plane so as tobe multiplied with said scene image, said grating comprising a pluralityof mutually coextensive azimuthally separated periodic arrays ofalternately opaque and neutral areas, said grating acting as a beamsplitter to produce distinct diffraction distributions along thedirection vectors of each of said azimuthally separated periodic arraysto form a radial spokelike composite diffraction distribution;

locating spectral filters having passbands characterizing differentspectral zones over the diffraction distributions associated with eachof said periodic arrays; collecting light passed by said spectralfilters and forming at a second image plane a second image of saidscene, representing the distribution at said first image plane asmodified by said grating and said spectral filters; and

recording said second image on a photosensitive material located at saidsecond image plane, the record thus formed comprising an additivesuperposition of color separation images defined by said spectralpassbands of said spectral filters, said color separation imagesrespectively modulating spatial carriers at different azimuthalorientations corresponding to the azimuthal orientations of saidperiodic arrays in said grating.

30. A method of color photography for recording color scenes onmonochrome or other recording materials which do not exhibit, whendeveloped, recorded color values in color, comprising:

erecting an aerial image of a scene to be photographed at a first imageplane; locating a grating at said first image plane so as to bemultiplied with said scene image, said grating comprising three mutuallycoextensive azimuthally separated periodic arrays of alternately opaqueand neutral areas, said grating acting as a beam splitter to producethree distinct diffraction distributions along the direction vectors ofeach of said azimuthally separated periodic arrays to form a radialspokelike composite diffraction distribution; locating red, blue, andgreen spectral filters respectively over said three diffractiondistributions associated with said three periodic arrays; collectinglight passed by said spectral filters and fonning at a second imageplane a second image of said scene, representing the distribution atsaid first image plane as modified by said grating and said spectralfilters; recording said second image on a photosensitive materiallocated at said second image plane, the record thus formed comprising anadditive superposition of red, blue, and green color separation imagesdefined by said spectral filters, said color separation imagesrespectively modulating spatial carriers at different azimuthalorientations corresponding to the relative azimuthal orientations ofsaid periodic arrays in said grating; locating said record in a beam ofsubstantially coherent light; forming in a Fourier transform space atleast one diffraction pattern of said record including three angularlyseparated Dirac delta function arrays respectively convolved withspectra of red, blue, and green color separation images; selectivelytransmitting at least one spectral order of each of said arrays throughsaid Fourier transform space; and causing the light carrying said red,blue, and green color separation information to be predominantly red,blue, and green, respectively, whereby a full color aerialreconstruction of said scene is produced.

31. A method of recording multicolor images on black-andwhite silverhalide photographic film by spectral zonal photogra hy for subsequentretrieval and display of said images in co or by spatial and spectralfiltering, wherein the recorded image has essentially no intrinsic colorother than black and white and carries color information in spatiallydistributed modulations of the recording image, compressing:

exposing a black-and-white substantially panchromatically sensitivephotographic film simultaneously to a self-registered plurality ofspectrally separated images of a multicolor scene formed 'in radiationpropagating from said scene, said images being separated into at leastthree separate zones of the visible light spectrum; during said exposureoperation, causing a spatially periodic light modulation function to bemultiplied with each of said spectrally separated images substantiallythroughout said image, said light modulation functions each having aunique azimuthal orientation which characterizes the spectrallyseparated image modulated thereby for separation in Fourier transformspace from the remainder of said images, the spatial frequency of eachof said light modulation functions being substantially twice as great asthe highest scene spatial frequency desired to be recorded in the imagemodulated thereby; and developing the thus exposed photographic film toform a composite record of said images each bearing its spatiallyperiodic modulation having said unique azimuthal orientation.

32. A method of recording multicolor images on black-andwhite silverhalide photographic film by spectral zonal photography for subsequentretrieval and display of said images in color by spatial and spectralfiltering, wherein the recorded image has essentially no intrinsic colorother than black and white and carries color information in spatiallydistributed modulations of the recorded image, comprising:

exposing a black-and-white substantially panchromatically sensitivephotographic film simultaneously to a self-registered plurality ofspectrally separated images of a multicolor scene formed in radiationpropagating from said scene, said images being separated into at leastthree separate zones of the visible light spectrum;

during said exposure operation, causing a'spatially periodic lightmodulation function to be multiplied with each of said spatiallyseparated images substantially throughout said image, said lightmodulation functions each having a unique azimuthal property whichcharacterizes the spectrally separated image modulated thereby forseparation in Fourier transfomi space from the remainder of said images,the spatial frequency of each of said light modulation functions beingsubstantially twice as great as the highest scene spatial frequencydesired to be recorded in the image modulated thereby; and

developing the thus exposed photographic film to form a composite recordof said images each bearing its spatially periodic modulation havingsaid unique azimuthal pro- P modulating with said record a beam of lightthat is substantially coherent; forming in a Fourier transform spacefrom said light as so modulated a diffraction pattern of said recordincluding a plurality, the same in number as said plurality ofspectrally separated images, of spatially separated Dirac delta functionarrays, each array being convolved with a spectrum of spatiallydispersed frequencies and characterizing a unique one of said spectrallyseparated images; selectively transmitting through said Fouriertransform space from each of said arrays the spectral zone correspondingto the spectral zone of the spectrally separated image characterized bysaid array; and retransforming light of said transmitted zones to thusproduce at an output space an aerial reconstruction of said multicolorscene.

1. Method of preparing a photostored record of a scene in a photostoragematerial which has response to light in a prescribed spectral band butdoes not make a color record within said band of the recorded light,which record is suitable for producing by Fourier transform and spatialand spectral filtering techniques an image of said scene in prescribedcolors which may be natural or artificial, which record is made from''''n'''' light components representing spectral zones within said bandof said scene where ''''n'''' is an integer greater than one, saidmethod comprising the steps of:
 1. erecting in an image plane an imageof said scene;
 2. modulating the light of said image in each of saidcomponents with a periodic function having a unique azimuthalorientation;
 3. selecting a modulating spatial frequency for each ofsaid light components which is substantially twice the highest scenespatial frequency desired to be reconstructed from that component; and4. forming in said photostorage material from the light of said image asso modulated a photostored record of the sum of the products of saidlight components each multiplied with its respective modulation. 2.Method according to claim 1 in which each of said periodic functions iscontained in a transmission grating which is located between said sceneand said photostorage material.
 2. modulating the light of said image ineach of said components with a periodic function having a uniqueazimuthal orientation;
 3. Method according to claim 2 in which saidgrating is located substantially in the image plane.
 3. selecting amodulating spatial frequency for each of said light components which issubstantially twice the highest scene spatial frequency desired to bereconstructed from that component; and
 4. forming in said photostoragematerial from the light of said image as so modulated a photostoredrecord of the sum of the products of said light components eachmultiplied with its respective modulation.
 4. Method according to claim3 in which the photostorage material is also located in the image plane,the grating is in contact with the photostorage material, and the imageis projected onto the photostorage material through the grating. 5.Method according to claim 3 in which a transform of the gratingconvolved with the image spectrum is spectrally filtered to form saidphotostored record.
 6. Method according to claim 3 in which eachperiodic function is a simple noncolor selective harmonic function, anda transform of the grating convolved with the image spectrum isspectrally filtered to form said photostored record.
 7. Method accordingto claim 2 in which the grating is a substantially two-dimensional lightfilter having a plurality of ''''n'''' periodic functions each extendingthroughout the area of said filter and having a unique azimuthalcharacteristic in the area of the filter for passing lightrepresentative of a unique wavelength band corresponding to a selectedone of said spectral zones, respectively, said functions overlappingeach other, the configuration of said functions being such that thelight transmittance of said filter is expressed as the product: Where:pi (x, lambda ) is the mathematical representation of the total filterwith transmittance a function of spatial coordinates x and wavelengthlambda ; P (x) is the periodic function corresponding to the wavelengthband lambda i with azimuthal characteristic lambda i; and lambda i isthe average wavelength in the band from lambda i-Delta lambda i tolambda i + Delta .
 8. Method of preparing a colorblind imagetransparency suitable for producing a projected image of a scene inprescribed colors, which may be natural or artificial, from ''''n''''light components representing spectral zones of light from said scenewhere ''''n'''' is an integer greater than one, comprising the steps ofproviding a film plane contact color modulation filter having aplurality Of ''''n'''' unique periodic functions, each of said functionshaving a unique azimuthal characteristic in the plane of the filter andcomprised of periodic color filter elements capable of passing lightlimited to a unique wavelength band corresponding to a selected one ofsaid light components, respectively, the configuration of said functionsbeing such that when the filter is transilluminated with an aerial colorimage of said scene the filter-color image product is expressed as:where the aerial color image Iw(x, lambda ) can be expressed as the sumof its spectral components: selecting a spatial frequency for each ofsaid periodic functions which is substantially twice the highest scenespatial frequency desired to be reconstructed from the light componentmodulated by that periodic function; and placing said filter in contactwith a photographic film which has panchromatic response to coloredlight but does not make a color record thereof; exposing said film tosaid image through said filter; and developing said film.
 9. Methodaccording to claim 8 in which said film is processed to provide atransparency in which the amplitude transmittance is substantiallylinearly proportional to the exposure.
 10. A method according to claim 1in which the photostored record is a transparency, including the furtherstep of so forming said transparency that when it is transilluminatedits output amplitude transmittance is substantially linearlyproportional to the input exposure which formed said record.
 11. Amethod according to claim 3 in which the image-grating product isreimaged onto said photostorage material to form said photostoredrecord.
 12. A method of spectral zonal photography comprising: exposinga photosensitive material responsive to radiation in all spectral zonesdesired to be recorded to an additive superposition of spectralseparation images formed in radiation propagating from a photographedscene in at least three different zones of the electromagnetic spectrum;during the said exposure operation, causing a periodic grating functionto be multiplied with each of said separation images, said gratingfunctions having a different azimuthal orientation for each image;selecting a spatial frequency for each of said grating functions whichis substantially twice the highest scene spatial frequency desired to bereconstructed from the spectral separation image multiplied with thatgrating function; and developing the exposed photosensitive material toform a record containing said separation images respectively modulatingazimuthally distinct spatial carriers.
 13. A method as defined by claim12 wherein said record comprises a photographic transparency and whereinsaid developing operation is such as to cause said transparency to havean amplitude transmittance characteristic which is substantiallylinearly proportional to the exposure which it received from theradiation forming said images.
 14. A method as defined by claim 12wherein said periodic arrays of filter elements are each spaced bysubstantially spectrally neutral elements, said filter elements in eacharray constituting a significantly greater fraction of the period widththan said neutral elements.
 15. A method of spectral zonal photography,comprising: exposing a photosensitive material responsive to radiationin all spectral zones desired to be recorded to a scene image multipliedwith a spectral zonal encoder comprising at least three mutuallycoextensive, azimuthally distinct periodic arrays of filter elementseach having a preferential absorption for a different spectral zone andthus each modulating a different color separation image; selecting aspatial frequency for each of said periodic arrays of filter elementswhich is substantially twice the highest scene spatial frequency desiredto be reconstructed from the color separation image modulated by thatarray; and developing the exposed photosensitive material to form arecord containing said color separation images respectively modulatingazimuthally distinct spatial carriers.
 16. A method of color photographyusing monochrome or other recording materials which do not exhibit, whendeveloped, recorded color values in color, comprising: exposing aphotosensitive material responsive to radiation in all spectral zonesdesired to be recorded to a scene multiplied with a spectral zonalfilter comprising mutually coextensive, azimuthally distinct periodicarrays of cyan, yellow, and magenta filter elements, said cyan, yellow,and magenta arrays respectively periodically modulating red, blue, andgreen color separation images; selecting a spatial frequency for each ofsaid periodic arrays of filter elements which is substantially twice thehighest scene spatial frequency desired to be reconstructed from thecolor separation image modulated by that array; and developing saidphotosensitive material to form a record containing red, blue, and greencolor separation images respectively modulating azimuthally distinctspatial carriers.
 17. A method as defined by claim 16 wherein saidrecord comprises a photographic transparency and wherein said developingoperation is such as to cause said transparency to have an amplitudetransmittance characteristic which is substantially linearlyproportional to the exposure which it received from the radiationforming said images.
 18. A method as defined by claim 16 wherein saidperiodic arrays of filter elements are each spaced by substantiallyspectrally neutral elements, said filter elements in each arrayconstituting a significantly greater fraction of the period width thansaid neutral elements.
 19. A method of spectral zonal photography andreconstruction, comprising: exposing a photosensitive material to ascene multiplied with a spectral zonal filter comprising three mutuallycoextensive, azimuthally distinct periodic arrays of filter elementseach having a preferential absorption for a different spectral zone andthus each modulating a different spectral separation image; selecting aspatial frequency for each of said periodic arrays of filter elementswhich is substantially twice the highest scene spatial frequency desiredto be reconstructed from the spectral separation image modulated by thatarray; developing said photosensitive material to form a recordcontaining three spectral separation images modulating azimuthallydistinct spatial carriers; locating the developed record in a beam oflight which is substantially coherent; forming in a Fourier transformspace a diffraction pattern of said record including three angularlyseparated Dirac delta function arrays, each array being convolved with aspectrum of spatial frequencies characterizing a different one of saidcolor separation images; selectively transmitting through said Fouriertransform space at least one spectral order of said spatial frequencyspectra associated with each of said color separation images; causingthe radiation passed through said transform space in each of saidspectral orders to have a mean wavelength consonant with the colorseparation information carried; and retransforming said transmittedspectra to thus produce at an output plane a full spectrum aerialreconstruction of the photographed scene.
 20. A method as defined byclaim 19 wherein said record comprises a photographic transparency andwherein said developing operation is such as to cause said transparencyto have an amplitude transmittance characteristic which is substantiallylinearly proportional to the exposure which it received from theradiation forming said images.
 21. A method as defined by claim 19wherein said periodic arrays of filter elements are each spaced bysubstantially spectrally neutral elements, said filter elements in eacharray constituting a significantly greater fraction of the period widththan Said neutral elements.
 22. A method of color photography andreconstruction using monochrome or other recording materials which donot exhibit, when developed, recorded color values in color, comprising:erecting a full color aerial image of a scene to be photographed at animage plane; locating a color encoding filter at said image plane so asto be multiplied with said scene image, said filter comprising threemutually coextensive, azimuthally separated periodic arrays of differentsubtractive primary filter elements, each periodic array modulating adifferent color separation image; selecting a spatial frequency for eachof said periodic arrays of filter elements which is substantially twicethe highest scene spatial frequency desired to be reconstructed from thecolor separation image modulated by that array; exposing aphotosensitive material to said image multiplied with said filter;developing said material to form a record of said scene in which red,blue, and green color separation images are effectively impressed onspatial carriers having different azimuthal orientations; locating thedeveloped record in light which is substantially coherent; forming in aFourier transform space at least one diffraction pattern of said recordincluding three angularly separated Dirac delta function arraysrespectively convolved with spectra of said red, blue, and green colorseparation images; selectively transmitting at least one spectral orderof each of said arrays through said Fourier transform space; and causingthe light carrying said red, blue, and green color separationinformation to be predominantly red, blue, and green, respectively,whereby a full color aerial reconstruction of said scene is produced.23. A method of color photography for recording color scenes onmonochrome or other recording materials which do not exhibit, whendeveloped, recorded color values in color, comprising: locating at arecording plane a photosensitive material responsive to radiation in allspectral zones desired to be recorded; effecting a multiple exposure ofsaid photosensitive material by, in succession, forming an image of saidphotographic object on said photosensitive material in radiation in eachof a plurality of spectral zones to which said photosensitive materialis responsive; during each of said multiple exposures of saidphotosensitive material, locating at said recording plane a gratinghaving a spatial frequency resolvable by said photosensitive material;selecting a spatial frequency for the grating for each exposure which issubstantially twice the highest scene spatial frequency desired to bereconstructed from the color separation image modulated by that grating;causing the grating to have a different relative azimuthal orientationduring each exposure of said photosensitive material; and developing themultiple latent color separation images thus formed in saidphotosensitive material to produce a record containing a plurality ofadditively superimposed color separation images each of which modulatesa spatial carrier having a different azimuthal orientation.
 24. A methodas defined by claim 23 wherein said record comprises a photographictransparency and wherein said development step is such as to cause saidtransparency to have an amplitude transmittance characteristic which issubstantially linearly proportional to the exposure which it receivedfrom the radiation forming said images.
 25. A method as defined by claim23 wherein said grating comprises a periodic array of alternately opaqueand neutral areas, the opaque area constituting a significantly greaterfraction of the period width than said neutral areas.
 26. A method ofcolor photography and reconstruction using monochrome or other recordingmaterials which do not exhibit, when developed, recorded color values incolor, comprising: locating at a recording plane a photosensitivematerial responsive to rAdiation in all spectral zones desired to berecorded; effecting a multiple exposure of said photosensitive materialby, in succession, forming an image of said photographic object on saidphotosensitive material in radiation in each of a plurality of spectralzones to which said photosensitive material is responsive; during eachof said multiple exposures of said photosensitive material, locating atsaid recording plane a grating having a spatial frequency resolvable bysaid photosensitive material; selecting a spatial frequency for thegrating for each exposure which is substantially twice the highest scenespatial frequency desire to be reconstructed from the color separationimage modulated by that grating; causing the grating to have a differentrelative azimuthal orientation during each exposure of saidphotosensitive material; locating the developed record in a beam oflight which is substantially coherent; forming in a Fourier transformspace a diffraction pattern of said record including three angularlyseparated Dirac delta function arrays, each array being convolved with aspectrum of spatial frequencies characterizing a different one of saidcolor separation images; selectively transmitting through said Fouriertransform space at least one spectral order of said spatial frequencyspectra associated with each of said color separation images;retransforming said transmitted spectra; causing the radiation passedthrough said transform space in each of said spectral orders to have amean wavelength consonant with the color separation information carried;and retransforming said transmitted spectra to erect at an output planea full color aerial reconstruction of the photographed scene.
 27. Amethod as defined by claim 26 wherein said record comprises aphotographic transparency and wherein said development step is such asto cause said transparency to have an amplitude transmittancecharacteristic which is substantially linearly proportional to theexposure which it received from the radiation forming said images.
 28. Amethod as defined by claim 26 wherein said grating comprises a periodicarray of alternately opaque and neutral areas, the opaque areaconstituting a significantly greater fraction of the period width thansaid neutral areas.
 29. A method of spectral zonal photography forrecording color values on monochrome or other recording materials whichdo not exhibit, when developed, recorded color values in color,comprising: erecting a full-color aerial image of a scene to bephotographed at a first image plane; locating a grating at said firstimage plane so as to be multiplied with said scene image, said gratingcomprising a plurality of mutually coextensive azimuthally separatedperiodic arrays of alternately opaque and neutral areas, said gratingacting as a beam splitter to produce distinct diffraction distributionsalong the direction vectors of each of said azimuthally separatedperiodic arrays to form a radial spokelike composite diffractiondistribution; locating spectral filters having passbands characterizingdifferent spectral zones over the diffraction distributions associatedwith each of said periodic arrays; collecting light passed by saidspectral filters and forming at a second image plane a second image ofsaid scene, representing the distribution at said first image plane asmodified by said grating and said spectral filters; and recording saidsecond image on a photosensitive material located at said second imageplane, the record thus formed comprising an additive superposition ofcolor separation images defined by said spectral passbands of saidspectral filters, said color separation images respectively modulatingspatial carriers at different azimuthal orientations corresponding tothe azimuthal orientations of said periodic arrays in said grating. 30.A method of color photography for recording color scenes on monochromeor other recorDing materials which do not exhibit, when developed,recorded color values in color, comprising: erecting an aerial image ofa scene to be photographed at a first image plane; locating a grating atsaid first image plane so as to be multiplied with said scene image,said grating comprising three mutually coextensive azimuthally separatedperiodic arrays of alternately opaque and neutral areas, said gratingacting as a beam splitter to produce three distinct diffractiondistributions along the direction vectors of each of said azimuthallyseparated periodic arrays to form a radial spokelike compositediffraction distribution; locating red, blue, and green spectral filtersrespectively over said three diffraction distributions associated withsaid three periodic arrays; collecting light passed by said spectralfilters and forming at a second image plane a second image of saidscene, representing the distribution at said first image plane asmodified by said grating and said spectral filters; recording saidsecond image on a photosensitive material located at said second imageplane, the record thus formed comprising an additive superposition ofred, blue, and green color separation images defined by said spectralfilters, said color separation images respectively modulating spatialcarriers at different azimuthal orientations corresponding to therelative azimuthal orientations of said periodic arrays in said grating;locating said record in a beam of substantially coherent light; formingin a Fourier transform space at least one diffraction pattern of saidrecord including three angularly separated Dirac delta function arraysrespectively convolved with spectra of red, blue, and green colorseparation images; selectively transmitting at least one spectral orderof each of said arrays through said Fourier transform space; and causingthe light carrying said red, blue, and green color separationinformation to be predominantly red, blue, and green, respectively,whereby a full color aerial reconstruction of said scene is produced.31. A method of recording multicolor images on black-and-white silverhalide photographic film by spectral zonal photography for subsequentretrieval and display of said images in color by spatial and spectralfiltering, wherein the recorded image has essentially no intrinsic colorother than black and white and carries color information in spatiallydistributed modulations of the recording image, compressing: exposing ablack-and-white substantially panchromatically sensitive photographicfilm simultaneously to a self-registered plurality of spectrallyseparated images of a multicolor scene formed in radiation propagatingfrom said scene, said images being separated into at least threeseparate zones of the visible light spectrum; during said exposureoperation, causing a spatially periodic light modulation function to bemultiplied with each of said spectrally separated images substantiallythroughout said image, said light modulation functions each having aunique azimuthal orientation which characterizes the spectrallyseparated image modulated thereby for separation in Fourier transformspace from the remainder of said images, the spatial frequency of eachof said light modulation functions being substantially twice as great asthe highest scene spatial frequency desired to be recorded in the imagemodulated thereby; and developing the thus exposed photographic film toform a composite record of said images each bearing its spatiallyperiodic modulation having said unique azimuthal orientation.
 32. Amethod of recording multicolor images on black-and-white silver halidephotographic film by spectral zonal photography for subsequent retrievaland display of said images in color by spatial and spectral filtering,wherein the recorded image has essentially no intrinsic color other thanblack and white and carries color information in spatially distributedmodulations of the recordeD image, comprising: exposing ablack-and-white substantially panchromatically sensitive photographicfilm simultaneously to a self-registered plurality of spectrallyseparated images of a multicolor scene formed in radiation propagatingfrom said scene, said images being separated into at least threeseparate zones of the visible light spectrum; during said exposureoperation, causing a spatially periodic light modulation function to bemultiplied with each of said spatially separated images substantiallythroughout said image, said light modulation functions each having aunique azimuthal property which characterizes the spectrally separatedimage modulated thereby for separation in Fourier transform space fromthe remainder of said images, the spatial frequency of each of saidlight modulation functions being substantially twice as great as thehighest scene spatial frequency desired to be recorded in the imagemodulated thereby; and developing the thus exposed photographic film toform a composite record of said images each bearing its spatiallyperiodic modulation having said unique azimuthal property; modulatingwith said record a beam of light that is substantially coherent; formingin a Fourier transform space from said light as so modulated adiffraction pattern of said record including a plurality, the same innumber as said plurality of spectrally separated images, of spatiallyseparated Dirac delta function arrays, each array being convolved with aspectrum of spatially dispersed frequencies and characterizing a uniqueone of said spectrally separated images; selectively transmittingthrough said Fourier transform space from each of said arrays thespectral zone corresponding to the spectral zone of the spectrallyseparated image characterized by said array; and retransforming light ofsaid transmitted zones to thus produce at an output space an aerialreconstruction of said multicolor scene.